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July 20, 2007 -- Reuters -- Britain's GW Pharmaceuticals announced a new delay for its pioneering cannabis-based medicine on Friday, saying European drug regulators had requested a further clinical study as a condition for approval.

Shares in GW, which has dispensation from the British government to use cannabis for medical research, plunged around a third in value as Chief Executive Justin Gover said the new study was likely to set back approval by 12 to 18 months. But he also told Reuters he was more confident that Sativex would win approval following the detailed talks with regulators.

"It's slightly regrettable that this produces something of a delay in the approval. But on the other hand, it makes us comfortable that the approval is even more certain than it was three or four months ago," he said in a telephone interview.

Sativex, which is sprayed under the tongue, became the first cannabis-derived medicine to win regulatory approval when it was approved in Canada in 2005 as a treatment for neuropathic, or nerve, pain in multiple sclerosis (MS) patients. But the drug has been hit by a string of delays in Europe, where GW originally hoped to win approval in 2003.

GW, which is seeking approval in Europe for Sativex as a treatment for spasticity in MS patients, said regulators wanted to be able to identify patients who responded in the first four weeks of treatment and confirm that improvements gained over a further 12 weeks were statistically greater than placebo.

The firm, which grows thousands of marijuana plants at a secret location in the English countryside, said it had provided statistical proof based on existing data, but that regulators wanted a new study specifically designed to meet their goals. Gover said GW was confident of producing favourable results.

"We feel that the analyses that we've done are very robust. They don't leave us with room for doubt that we can reproduce these because the results we've had are very impressive."

GW said it expected to complete the new study in the second half of 2008, but that it might be able to resubmit Sativex to European regulators before then as a treatment for neuropathic pain in MS patients if separate trial results in this therapeutic area, due early next year, are favourable. The new study in MS spasticity would be funded from the firm's existing budget for 2008, GW said in a statement.

GW Pharmaceuticals, which makes medicines based on cannabis, came out vociferously defending its pioneering drug today after it was forced to admit a recent trial had disappointed and its shares fell sharply as a result.

Shares in the Salisbury-based firm slumped more than 30% in early trading after it said a trial of its Sativex drug to treat pain in multiple sclerosis showed an "unexpected" response to a placebo.

The company insisted the drug's efficacy was not called into question but the news sparked doubts in the market over whether GW Pharma's flagship product will become a commercial success.

The company said in a statement to the stock exchange that although the patient response rate to its drug, sprayed into a patient's mouth, was "very high" and better than the placebo, the difference between the two was insufficient. That meant the trial was unable to yield a "statistically significant outcome".

"Although the difference between the Sativex and placebo groups was clearly in favour of Sativex, it narrowly failed to reach statistical significance in this trial due to an unexpectedly large placebo response," GW Pharma explained.

It added that in the trial patients were able set dosages themselves in order to look for the optimum level but that such a design "appears to have encouraged an abnormally high placebo response".

The research will not detract from any previous positive trials on using Sativex for MS pain or other types of pain, said managing director Justin Gover, but GW Pharma will have to scrap these results and perform a new trial.

"Accidents do happen in clinical trials and pain research in particular is vulnerable to placebo responses. What we have seen in this study is that patients benefit hugely from our drug, that's not in question," said Gover. "But the extent of the placebo response confounds the interpretation of the undoubted benefit seen on Sativex.

"This doesn't call into question anything we have seen before but it doesn't show anything new. So we have to put it to one side and do another trial."

The company said other trials on Sativex for other symptoms were not affected by this result. But the market was unsettled by the news and although GW Pharma's shares recovered somewhat after the initial slump they were still down 16.5p, or 23%, at 55p in late trading.

KBC Peel Hunt analyst Paul Cuddon commented that "this indicates that the effect of Sativex is marginal, and we retain our doubts as to whether the product will ever prove a commercial success".

GW Pharma has been developing Sativex for 10 years, working with government backing to develop a safe way to provide cannabis-based pain relief. It grows thousands of marijuana plants at a secret countryside location to help develop the drug that provides relief for MS pain, MS muscle stiffness, or spasticity, cancer pain and nerve damage pain caused by conditions such as shingles and diabetes.

The drug became the first cannabis-derived medicine to win regulatory approval when it was approved in Canada in 2005 as a treatment for nerve pain in MS patients and it is also available in the UK on special prescriptions.

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